There is intensive research worldwide aimed at the utilization of natural gas as a petrochemical feed stock. The current use of natural gas is mainly restricted to the production of synthesis gas ("syngas", a mixture of carbon monoxide and hydrogen), and heat.
It has been long known, however, that methane can be converted to acetylene containing synthesis gas mixtures using short contact time acetylene burners. Co-producing ethylene or mixing ethylene with these acetylene rich feeds could provide a cheap, natural gas based feed stock. However, use of such coproduced feed streams has presented problems in certain processes.
Hydroformylation of highly purified olefins and syngas mixtures to aldehyde and alcohol products is well known (see B. Cornils "Hydroformylation. Oxo Synthesis, Roelen Reaction" in "New Syntheses with Carbon Monoxide", Ed. J. Falbe, Springer Verlag: New York, 1980). When pure alcohol products are desired, the aldehyde products can be hydrogenated to the corresponding alcohol derivatives. A particularly useful catalyst has been described for the hydroformylation of pure light olefin feeds as a homogeneous oil soluble phosphine modified Rh catalyst (see, e.g., U.S. Pat. Nos. 3,527,809, 3,917,661, 4,148,830) which operates at lower pressures than other homogeneous catalysts, gives high normal to iso ratios in the hydroformylation of C.sub.3 and higher olefins, and has been proven to be very effective with those pure olefin feeds. The use of such an oil soluble homogeneous Rh catalyst to hydroformylate purified ethylene feeds to propanal has been also described by Evans et al (J. Chem. Soc. (A) 1968, 3133), as well as Pruett et al (J. Org. Chem. 1968, 34, 327). There is a great need, however, for a stringent purification of the feed stock, because the activity of the catalyst is strongly inhibited by acetylene and other highly unsaturated hydrocarbons if they are present as impurities in commercial oxo feeds. These components must essentially be removed before hydroformylation (see B. Cornils "Hydroformylation. Oxo Synthesis, Roelen Reaction" in "New Syntheses with Carbon Monoxide", Ed.: J. Falbe, Springer Verlag: New York, 1980, pp. 64 and 73).
Highly purified feeds of syngas (mixtures of CO and H.sub.2) and olefins are currently made in two separate processes. Light olefins are usually made by steam cracking and purified by cryogenic distillation and selective hydrogenation to remove even traces of acetylenes and dienes. The currently used highly purified olefin feeds contain less than 100 ppm and typically less than 10 ppm of these impurities. In fact, a large portion of the cost of ethylene currently produced for hydroformylation by steam cracking is associated with its purification. The syngas component can be made from a hydrocarbon, such as methane or a crude distillate, and oxygen in a partial oxidation (POX) reactor run in a mode that produces essentially no dienes or acetylenes. Even though the syngas made in the POX reactor contains only trace amounts of acetylenes and dienes it is also carefully further purified before being blended with the purified olefin feed.
Hydroformylation of pure acetylenes and of pure dienes with Co or Rh catalysts is also known. (see: U.S. Pat. No. 5,312,996, 1994; P. W. N. M. Van Leeuwen and C. F. Roobeek J. Mol. Catal. 1985; U.S. Pat. No. 4,507,508, 1985; 31, 345, B. Fell, H. Bahrmann J. Mol. Catal. 1977, 2, 211; B. Fell, M. Beutler Erd ol und Kohle--Erdgas--Petrochem. 1976, 29 (4), 149; U.S. Pat. No. 3,947,503, 1976; B. Fell, W. Boll Chem. Zeit. 1975, 99(11),452; M. Orchin, W. Rupilius Catal. Rev. 1972, 6(1), 85; B. Fell, M. Beutler Tetrahedron Letters 1972, No. 33, 3455; C. K. Brown and G. Wilkinson J. Chem. Soc. (A) 1970, 2753; B. Fell, W. Rupilius Tetrahedron Letters 1969, No. 32, 2721; F. H. Jardine et al Chem. and Ind. 1965, 560; H. Greenfield et al J. Org. Chem. 1957, 22, 542; H. Adkins and J. L. R. Williams J. Org. Chem. 1952, 71, 980). The hydroformylation of these highly unsaturated compounds with cobalt catalysts is slow even at high temperatures and pressures (145.degree.-175.degree. C., 20-30 MPa). Furthermore, the reaction often yields side products and results in runaway reactions with sudden temperature and pressure surges. The hydroformylation of olefins is severely inhibited by acetylenes since these compounds form very stable adducts with cobalt carbonyl. Stoichiometric amounts of acetylenes can effectively transform the cobalt catalyst into these catalytically inactive acetylenic adducts (H. Greenfield et al. J. Org. Chem. 1957, 22, 542). With conventional Rh catalysts the reported reaction conditions and reaction rates are far from being practical for any commercial use. Fell typically used 17-23 MPa pressures using PPh.sub.3 /Rh catalyst, yet high conversions required 2 to 5 hour reaction times. Wilkinson achieved high conversion in the hydroformylation of hexyne-1 at 4.8 MPa pressure but only with a reaction time of 12 hours. Van Leeuwen and Roobeek applied conditions of 1.2 MPa, 95.degree.-120.degree. C., and P/Rh ratios of 10 or below in the hydroformylation of butadiene but observed low activities (orders of magnitude below that for olefins). In U.S. Pat. No. 3,947,503 a two stage process is described to hydroformylate 1,3-butadiene. In the first stage PPh.sub.3 /Rh catalyst is used in the presence of alcohols or diols to make the acetals of the unsaturated C.sub.5 -aldehyde. In the second stage this intermediate is hydroformylated using Co catalysts. The process disclosed in U.S. Pat. No. 4,507,508 also claims the conversion of conjugated dienes with organic acid or ester promoted P/Rh catalyst in the presence of alcohols. U.S. Pat. No. 5,312,996 describes a polyphosphite ligand modified Rh catalyst for the conversion of 1,3-butadiene. When using a two stage process for the hydroformylation of 1,3-butadiene with the disclosed catalyst more severe conditions are recommended in the second stage to ensure acceptable conversions. This later patent also describes 1,3-butadiene as a strong inhibitor in the conversion of alpha-olefins. In the co-conversion of alpha-olefins with 1,3-butadiene oxo aldehyde products of both the alpha-olefins and 1,3-butadiene were produced.
As mentioned, acetylenes and dienes act as strong inhibitors/poisons of catalysts in the hydroformylation of alpha-olefins and their removal is required from oxo feeds. European Patent Application No. 0225 143 A2 discloses a method for the production and utilization of acetylene and ethylene containing syngas mixtures. One of the disclosed utilization schemes is to produce propanal by hydroformylation, but acetylene first must be removed from the feed by selective hydrogenation to ethylene over a heterogeneous metal oxide or sulfide catalyst. U.S. Pat. No. 4,287,370 also teaches that inhibitors such as 1,3-butadiene must be removed from C.sub.4 -olefin feed stocks by selective hydrogenation prior to hydroformylation using HRh(CO)(PPh.sub.3).sub.3 as a catalyst. German patent, DE 2638798, teaches that the removal of acetylenes and dienes is necessary in order to ensure acceptable catalyst life in the hydroformylation of olefins with a phosphine modified rhodium catalyst. In one of the most often cited sources (B. Cornils "Hydroformylation. Oxo Synthesis, Roelen Reaction" in "New Syntheses with Carbon Monoxide", Ed.: J. Falbe, Springer Verlag: New York, 1980, p. 73) acetylenes and dienes are referred to as "classical catalyst poisons" for the phosphine modified Rh oxo catalysts. Acetylenes and dienes are also reported to be strong poisons in the hydroformylation of olefins with cobalt catalysts (V. Macho and M. Polievka Rau. Roc. 1976, 18(1), 18; U.S. Pat. No. 2,752,395).
Known catalytic processes converting acetylene and ethylene containing syngas mixtures either produce products other than propanal or the conditions used and/or the reaction rates achieved are far from being practical. Thus, for example, European Patent Application No. 0,233,759 (1987) teaches the conversion of acetylene and ethylene containing syngas (a mixture of acetylene, ethylene, CO, and H.sub.2 with a ratio of 6:3:30:61, respectively) into a mixture of acrylate and propionate esters in the presence of an alcohol using a Rh catalyst. When using a PPh.sub.3 modified Rh oxo catalyst to convert the same feed at a P/Rh ratio of 10.6 under otherwise identical conditions, the essentially dead catalyst (turnover frequency of 1.5.times.10.sup.-4 mol product/mol Rh/sec, and total turnover of 13 in 24 hours) described in European Patent Application No. 0,233,759 (1987) produces some propanal and acetone in a molar ratio of 90 to 1 with traces of methyl ethyl ketone and methyl propionate. It has been reported by T. Mise et al. (Chem. Lett. 1982, (3), 401) that syngas mixtures containing acetylene and ethylene yield a,b-unsaturated ethyl ketones in the presence of a Rh catalyst, however, no phosphine is present in the catalyst. Observed catalyst activities are very low, on the order of 5 turnover/h, or 1.39.times.10.sup.-3 mol product/mol Rh/sec even though the concentration of ethylene in the gas feed is high, 41.7 v. %. The total turnover reported by Mise is only 30 in 6 hours.
Thus it would be desirable if methods could be found to enable the processing of oxo/hydroformylation feed streams using rhodium based catalysts that contain olefins and alkynes, particularly ethylene and acetylene. The present invention addresses these needs.